1. Field of the Invention
The present invention relates generally to conduits for apical cannulation of the heart, and more specifically, to inflow cuffs for cannulation of the heart for ventricular assist device placement.
2. Description of Related Art
In the past, a patient requiring a heart transplant was forced to wait and hope that a suitable heart became available before he or she became too sick to undergo a transplant procedure. More recently, devices known as ventricular assist devices (VADs) have been developed. These devices are implantable, programmable pumps that assist the ventricles of the heart, usually the left ventricle, in pumping blood. The VAD presents both the physician and the patient with an alternative to the wait-and-hope approach of the past by allowing patients to be temporarily supported while awaiting transplant. Patients in whom a VAD has been implanted are typically healthy enough to undergo a transplant when a suitable heart becomes available. Studies have also shown that a VAD may be used for longer periods of time, e.g., more than a year.
However, the procedure to implant a VAD is a cardiothoracic surgical procedure, and as such, presents its own risk of complications. In a typical VAD implantation procedure, a xe2x80x9cside-bitingxe2x80x9d clamp is applied to the aorta and the outflow conduit from the VAD is sewn into the aorta. A vascular clamp is placed across the distal portion of the outflow conduit after the xe2x80x9cside-bitingxe2x80x9d clamp is removed in order to de-air the outflow conduit. Once the VAD outflow conduit is attached to the aorta, the inflow conduit is inserted into the apex of the heart. To place the inflow conduit, a hole is cored in the apex of the heart, and pericardial sutures are placed around the hole. After pericardial sutures are placed around the hole cored in the apex, an inflow cuff is inserted into the hole.
The inflow cuff is a short, relatively rigid connector that serves as an interface between the inflow conduit of the VAD and the ventricle. The inflow cuff is usually made of a biocompatible elastomer or plastic, such as silicone, which has been reinforced with a woven mesh. The woven mesh may be comprised of, e.g., woven polyester strands, and serves to rigidify the inflow cuff. A sewing ring made of synthetic felt (e.g., felt composed of poly(tetrafluoroethylene) or polyester strands) is typically provided around the external diameter of the inflow cuff so that the inflow cuff can be secured in the apex hole using the previously positioned pericardial sutures.
After the inflow cuff has been sewn into the apex of the heart, the inflow conduit from the VAD is passed through the inflow cuff and into the ventricle. The inflow cuff and inflow conduit are sized so that the inflow cuff has an internal diameter only slightly larger than the external diameter of the inflow conduit. Once the inflow conduit is inserted into the inflow cuff, the two form a snug fit such that there is essentially no clearance between the inflow conduit and inflow cuff. A simple tie-down is secured around the outer diameter of the inflow cuff to hold the inflow conduit in place.
Following the successful insertion of the inflow conduit into the inflow cuff, blood is permitted to egress the VAD via the outflow conduit and the heart is de-aired. Once the heart has been de-aired, the VAD is turned on and begins to operate.
Although the typical VAD implantation procedure uses an inflow cuff, as described above, to cannulate the apex of the heart, various other devices are known for apical cannulation of the heart, establishing access to the coronary vessels, or controlling blood flow from the heart.
For example, U.S. Pat. No. 4,769,031 to McGough et al. discloses a ventricular access device which is comprised of a conduit and grommet that are inserted into the base of the heart and fed though to the apex such that the left ventricle is cannulated in an inside-to-outside manner. The conduit includes a sharpened, retractable, conical end to facilitate penetration of the left ventricle and a grommet to hold the conduit in place. The grommet disclosed by this patent is complex, and the device has found little clinical applicability.
U.S. Pat. No. 6,053,896 to Wilson et al. discloses an apparatus suitable for a left ventricular drain line. The apparatus includes a duck-bill check valve to avoid pressure overload. The check valve opens in an outward direction to prevent blood from flowing back towards the heart. The apparatus is designed for extracorporeal use only; it does not include structure suitable for cannulation of the left ventricle.
Other devices available include that disclosed by U.S. Pat. No. 5,984,956 to Tweden et al., which describes an alternate type of apparatus for establishing blood flow between a chamber of the heart and one of the coronary vessels. The apparatus is a rigid conduit tube with a beveled end to aid in the penetration of cardiac tissue. It includes neither valve nor trocar, and there is no mention that backflow of blood into the heart may be a problem.
A more generally applicable device is disclosed by U.S. Pat. No. 5,830,222 to Makower, which describes a device and method for transvascular access. The disclosed method and device allow the vascular system to be used as a conduit for other procedures. Additionally, a number of hemostasis-type valves are known for arterial catheterization. However, none of these devices appears to designed for implantation directly into the heart.
A major difficulty with the typical VAD implantation procedure, and most other procedures requiring apical cannulation, is that the heart must be stopped, which requires that the patient be placed on cardiopulmonary bypass (CPB). If the heart is beating while the procedure is performed, the patient will exsanguinate (i.e., a large volume of blood will escape through the inflow cuff before the inflow conduit can be placed). Unfortunately, CPB carries with it an inherent risk of mortality, a risk that is especially acute in a critically ill patient requiring a VAD. Therefore, a need exists for an improved means of implanting a VAD without requiring the use of CPB.
One aspect of the claimed invention relates to an inflow cuff for beating-heart apical cannulation of a heart. The inflow cuff comprises a tube having a first end and a second end. The first end of the tube is constructed and adapted to be inserted into the heart. A sewing ring is disposed on an exterior surface of the tube proximate to the first end. The sewing ring is constructed and adapted to be sutured to an exterior wall of the heart and to retain the first end of the tube at a selected position in the heart. The inflow cuff also comprises a valve disposed on and integral with the interior of the tube. The valve has two or more compliant leaves constructed and adapted to form a releasable seal with one another. The valve prevents blood flow out of the heart when closed and opens in response to pressure directed towards the heart. The valve is disposed further from the first end of the tube than the sewing ring. Additionally, the inflow cuff is constructed and arranged to allow the passage of a trocar through its lumen, wherein the trocar is constructed and arranged to form a hole in the heart of sufficient size to admit the first end of the inflow cuff. The inflow cuff is further constructed and arranged to permit the withdrawal of the trocar and the insertion of a conduit through the lumen of the inflow cuff to establish a route for blood flow out of the heart.
Another aspect of the claimed invention relates to a medical device which may be inserted into the heart of a patient to provide a passageway for bloodflow, specifically bloodflow in a conduit. The medical device comprises an inflow cuff with a valve. The valve prevents blood from flowing out of the heart when closed and opens in response to pressure in the lumen of the inflow cuff directed inward toward the heart. The claimed invention also includes a trocar which is inserted longitudinally through the lumen of the inflow cuff and extends beyond the end of the inflow cuff. The trocar is removable from the lumen of the inflow cuff. The lumen of the inflow cuff is sized to allow the insertion of a conduit into the heart.
A further aspect of the claimed invention relates to a method for providing a passageway for bloodflow out of the heart of a patient. The method comprises inserting an inflow cuff according to the claimed invention into the heart, retracting the blade of the trocar and removing it from the inflow cuff and inserting an inflow conduit through the lumen of the inflow cuff to open the valve. The valve may be a unidirectional or an omni-directional valve. The inflow conduit inserted may be the inflow conduit of a ventricular assist device (VAD).